1. Field of the Invention
The present invention relates to disk drives. More particularly, the present invention relates to disk drives that include a base that contributes to reducing disk flutter induced track misregistration (xe2x80x9cTMRxe2x80x9d).
2. Description of the Prior Art
A typical hard disk drive includes a head disk assembly (xe2x80x9cHDAxe2x80x9d) and a printed circuit II board assembly (xe2x80x9cPCBAxe2x80x9d). The HDA includes at least one magnetic disk (xe2x80x9cdiskxe2x80x9d), a spindle motor for rotating the disk, and a head stack assembly (xe2x80x9cHSAxe2x80x9d) that includes a slider with at least one transducer or read/write element for reading and writing data. The HSA is controllably positioned by a servo system in order to read or write information from or to particular tracks on the disk. The typical HSA has three primary portions: (1) an actuator assembly that moves in response to the servo control system; (2) a head gimbal assembly (xe2x80x9cHGAxe2x80x9d) that extends from the actuator assembly and biases the slider toward the disk; and (3) a flex cable assembly that provides an electrical interconnect with minimal constraint on movement.
A typical HGA includes a load beam, a gimbal attached to an end of the load beam, and a slider attached to the gimbal. The load beam has a spring function that provides a xe2x80x9cgram loadxe2x80x9d biasing force and a hinge function that permits the slider to follow the surface contour of the spinning disk. The load beam has an actuator end that connects to the actuator arm and a gimbal end that connects to the gimbal that supports the slider and transmits the gram load biasing force to the slider to xe2x80x9cloadxe2x80x9d the slider against the disk. A rapidly spinning disk develops a laminar airflow above its surface that lifts the slider away from the disk in opposition to the gram load biasing force. The slider is said to be xe2x80x9cflyingxe2x80x9d over the disk when in this state.
FIG. 1 is an exploded perspective view of a conventional disk drive 10. As shown, the disk drive 10 includes a HDA 12 and a printed circuit board assembly PCBA 14. The HDA 12 includes a disk drive base 16 and a cover 18 that collectively house magnetic disks 20, 22, 24. Each magnetic disk 20, 22, 24 contains a plurality of tracks for storing data. The magnetic disks 20, 22, 24 may be two-sided, and thus for example, the magnetic disk 24 is shown having a track 26 on an upper facing side and a track 28 (shown in phantom) on a lower facing side. The head disk assembly 12 further includes a spindle motor 30 for rotating the magnetic disks 20, 22, 24. The head disk assembly 12 further includes a HSA 32 and a pivot-bearing cartridge 34. The head stack assembly 32 includes a rotary actuator 36.
The rotary actuator 36 includes an actuator body 38 that has a bore and the pivot-bearing cartridge 34 engaged within the bore for facilitating the rotary actuator 36 to rotate between limited positions. The rotary actuator 36 further includes a coil portion 40 that extends from one side of the actuator body 38 to interact with a pair of permanent magnets 42 to form a Voice Coil Motor (VCM) for pivoting the rotary actuator 36. A plurality of actuator arms, the lowermost one of which being denoted 44, extend from an opposite side of the actuator body 38. As the disks 20, 22, 24 may be two sided, each of the actuator arms is attached to either one or two head gimbal assemblies associated with the adjacent sides of the disks 20, 22, 24. Each head gimbal assembly includes a head (the uppermost one being denoted 46) for reading and writing data to and from a respective recording surface of one of the respective disks 20, 22, 24.
A challenge faced by hard disk drive designers and manufacturers as they continually increase the capacities of contemporary hard disk drives is the phenomenon known as non repeatable run out (xe2x80x9cNRROxe2x80x9d). Run out, either written into the servo tracks (usually denoted RRO) or occurring live during drive operation (NRRO), manifests itself as radial displacements of the read/write head(s) relative to the data tracks of the disk(s), caused by vibrations of either the HSA or disk pack (inc. spindle motor, disk(s), spacer(s), and clamp). As the storage capacity of magnetic disks increases, the number of data tracks per inch (xe2x80x9cTPIxe2x80x9d) is increased, or conversely, the track width is decreased, leading to greater data density per unit area on the magnetic media. Since NRRO may degrade the data transfer performance to and from the magnetic media by increasing, for example, the frequency of off track errors, the ratio of root mean square (RMS) NRRO to track width must be maintained at a fairly constant value; thus, designers must ensure that NRRO decreases in proportion to track width.
Airflow within a hard disk drive may be divided into three regions, each characterized by different properties. The first region is located near the hub of the disk pack, where the relatively slow moving air develops an irregularly shaped core of laminar airflow. The second region""s boundary ranges from the laminar core of the first region nearly to the OD of the disk. The higher velocity airflow within the second region is turbulent, particularly at the boundary with the first region. During operation, the heads must travel into and out of the irregularly shaped core of laminar airflow. The higher velocity of the airflow at and near the OD of the disk creates a vacuum-like effect and the pressure differences in the radial direction drive the air to flow unevenly outward, toward the OD of the disk and the third region.
The third region is the smallest of the three regions and yet is an important contributor to disk flutter induced TMR, which is the radial position error between the read/write transducer heads and the data track of a hard disk drive due to disk vibrations. The third region is bounded by the OD of the rotating disk(s) and the stationary shroud that defines the disk pack region of the base of the hard disk drive. This interface causes turbulent airflow that creates a great many small vortices near and against the shroud. Such vortices form by the interaction of the high speed developed by the air at the OD of the rotating disk, the stationary shroud and the viscous property of the air. If such turbulent airflow around the OD of the disk could be reduced, the component of TMR due to disk flutter could be reduced, with positive effects upon drive performance.
FIG. 2 is a perspective view of a conventional disk drive base 16. As shown therein, once the airflow (shown at reference numeral 202) induced by the rotating disks leaves the disk pack area 212, it also exerts an unsteady force on the HSA (shown in dashed lines at 32) and particularly on the actuator arms 44 thereof, which degrades the ability of the HSA 32 to precisely perform seek and track following operations. If the pattern of such airflow 202 could be modified so as to redirect it away from the HSA 32 and the actuator arms 44, the heads thereof may be controllable to a greater degree of precision than conventionally possible.
What are needed, therefore, are disk drives that are configured to reduce disk flutter induced TMNR. Also needed are disk drives in which the HSA resonances due to airflow are reduced.
Accordingly, this invention may be regarded as a disk drive, including: a base, the base defining a first interior surface and a second interior shroud surface that rises perpendicularly to the first interior surface; a disk; a spindle motor attached to the base for rotating the disk and a head stack assembly pivotally coupled to the base. The second interior surface is configured to follow a portion of the curvature of the disk at a distance from an outer diameter (OD) of the disk, the second interior shroud surface of the base defining a channel for modifying airflow developed as the disk rotates.
The disk drive may include a plurality of disks and the second interior shroud surface may define a channel for each of the plurality of disks. The disk drive may include a plurality of facing disks and the second interior shroud surface may define a channel between each two facing disks. The disk drive may define an outer diameter edge and the channel may be offset from the outer diameter edge. The disk may define an outer diameter edge and the channel may be aligned with the outer diameter edge. The channel may be configured to reduce turbulent airflow around the outer edge of the disk. The channel may run the entire length of the second interior shroud surface or a portion thereof. The channel may be continuous or may be discontinuous. The channel may define a regular or irregular cross-section.
According to another embodiment thereof, the present invention is a disk drive, comprising: a base, the base defining a first interior surface and a second interior shroud surface that rises perpendicularly to the first interior surface; a disk; a spindle motor attached to the base for rotating the disk, and a head stack assembly pivotally coupled to the base. The second interior surface is configured to follow a portion of the curvature of the disk at a distance from an outer diameter of the disk, the second interior shroud surface of the base defining an opening to enable the head stack assembly to pivot over the disk, the opening being bounded by a leading shroud portion and a trailing shroud portion, at least one of the leading shroud portion and the trailing shroud portion defining a channel for modifying airflow developed as the disk rotates.
The channel may be bounded by the first interior surface and a leading shroud portion surface that faces the first surface. A plurality of channels may be defined in the leading shroud portion. The channel may be bounded by the first interior surface and a trailing shroud portion surface that faces the first surface. A plurality of channels may be defined in the trailing shroud portion. The channel defined in the leading shroud portion may be shaped so as to redirect the airflow away from the head stack assembly. The channel defined in the trailing shroud portion may be shaped so as to redirect away from the head stack assembly.
The foregoing and other features of the invention are described in detail below and set forth in the appended claims.